I can't find any post detailing Screwfix or B&Q returns being auctioned off by the pallet load on here.When did you find it and which member posted it?Meanwhile you might find this helpful Here

21st Nov 2017

from my previous experience of buying these type of things the company selling wont normally give you information of where the items have been sourced from. you can usually check the manifest for each pallet and sometimes work out where they are from.